The invention relates to a bumper and in particular to the attachment of a bumper at a front end carrying structure or of a vehicle frame for absorbing deformations upon impact so as to prevent damage to the front end beam of the vehicle frame.
From the prior art DE 197 44 274A1, a bumper is known which is configured as an extruded profile attached to a longitudinal beam (front end beam) of the vehicle, where the bumper is mounted to the longitudinal beam. The end portions of the extruded profile of the bumper, which are connected to the longitudinal beam, are configured as crash absorbing elements and can absorb impacts up to 15 km/h in a so-called solid wall test. In such a test, vehicles are driven against a wall at the above-mentioned speed. Although this extruded profile fulfills all legal requirements prescribed in regulation EWG96/76 EG for the solid wall tests, the bumper disclosed in DE 197 44 274A1 both, that is, the extruded profile as well as the bumper mounted thereon are necessary for its functioning and requires assembly of at least two parts and thus resulting in a comparatively high overall weight.
EP 06 64 244A1 discloses a shock absorbing element used as an inlay between the external skin of the bumper and the vehicle beam with at least one shock absorbing rib. The rib comprises two spring legs, with each spring leg consisting of an impact transfer portion, an attachment portion and a curved portion impact absorption section connecting the impact transfer portion and the attachment portion. The spring legs are connected to each other in the area of the impact transfer portion. The distance of the two undeformed opposite spring legs is smaller in the impact-transfer-portions-proximate area than in the attachment-portions-proximate area of the impact absorption portions. In EP 06 64 244A1 a shock absorbing element absorbs a series of smaller impacts exhibiting an elastic deformation behavior at impact speeds over 4 km/h.
In the area close to the attachment portion, the spring legs extend along an attachment support and the curved attachment portions are directed away from the attachment support so that under a compressive stress acting upon the spring leg, areas of the curved shock absorbing portions are bearing increasingly upon the attachment base in a roll-off motion, thereby lowering their respective radius of curvature.
Since the rib is formed from two connected curved spring legs, which, in the area of the attachment portion, bear flat upon an attachment base, such as a beam or an outer surface of the bumper, and facing away form the attachment base are curved inwardly, further sections of the curved shock absorbing area are rolled onto the attachment surface under increasing impact force. The impact energy is thus dissipated by a successive rolling movement of the spring legs, whereby the deformation does not occur solely along a single buckling line but along a broad, 2-dimensional portion of the spring leg. Thus, a damper element which can withstand multiple impacts of a comparatively high force without loss of elasticity and without material fatigue is realized. However, the disclosed bumper works well for the shock absorption of low speed impact.
DE 41 10 436A1 discloses and describes mounting a bumper onto a longitudinal beam or a front-end beam. Deformation resistance of any part of the bumper is not disclosed, which implies, subjecting the disclosed single-piece bumper on the longitudinal beam or the front end beam to any force, will lead directly to a deformation of said beams. As a consequence higher costs for replacement or repair are experienced, since any impact, even a low speed impact, may cause damages to the bumper as well as the bumper beam.
EP 06 50 868A1 discloses a means of attachment for a bumper in the shape of a deformable mounting bracket. The bracket will deform as a consequence of an impact when the vehicle moves in frontal direction (x-coordinate), but nothing is disclosed about any lateral impact (x and y coordinates or y coordinate only).
DE 19511868A1 discloses a bumper with a bending beam, which is provided with crash absorbing elements. The bending beam is integrally connected with the crash absorbing elements, which extend at a right angle. The crash absorbing elements are provided with flanges, which serve as a connection with a longitudinal beam. The bending beam and the integrally connected crash absorbing elements are configured as two shells. For production-technical reasons it is not possible, to manufacture unitary bending beams and crash absorbing elements. The two shells must be assembled prior to incorporation whereby the assembly is carried out by means of techniques such as welding, pressure joining, gluing, riveting or screwing. Thus, at a normal drive speed, any impact will certainly be absorbed through the bending beam and the deformation elements, however the production of the bending beams is rather complex due to the additional production steps of assembling the shells.
In order to protect the bending beam properly—against shock impact at a low drive speed—it is necessary to provide an impact absorber at the front side of the bending carrier.
Thereby it is realized that the bending carrier absorbs impacts up to 15 km/hr, which however requires an assembly of at least five building elements, such as a bumper, two bending carrier shells and two impact absorbers. In addition, the bending beam is made of metal and exhibits no elasticity, so that for even small impacts an elastic yielding cannot be realized. Accordingly, when the bumper cannot deform in an elastic manner, there subsists the danger of damage to the bumper even upon very small impact. Whereas damage of this type may not always render the bumper unsuitable for use, it spoils the optical impression of the vehicle.
Likewise with the bumper disclosed in DE 19511868A1, the bumper disclosed in DE 298 239 73U1 includes several assembly parts, wherein even the profiled body and each of the crash absorbing elements are configured as separate parts. Impacts are introduced at the bumper into the metal sheet (or form part). In its function and arrangement, this metal sheet corresponds to the bending beam as disclosed in DE 19511868A1.
In laid open publication DE 19904879A1 it is envisioned that with changes in the wall thickness in the bumper beam with the use of the deformation elements, the level of force can be dissipated across the entire cross section of the bumper. The wall thickness of the inner walls of the crash absorbing elements is thus substantially inferior to the wall thickness of the exterior sidewall of the hollow profiled deformation elements. When the force level, which is composed of the longitudinal force and the bending stress is homogenized, three-dimensional extensions of the inner side of the longitudinal carrier are avoided. Thus, due to the inferior wall thickness of the crash absorbing elements, the transverse carriers will buckle or fail before the transverse beam deforms in a three-dimensional manner with a definite impact force. This solution is advantageous, if the crash absorbing element is easily dismantled from the bumper but not disclosed in this publication and made obvious only through DE 29823973U1. When the crash absorbing elements are integrally formed with the bumper beam, both bumper beam and crash absorbing element must be replaced, if the impact does not result in a deformation in an elastic range. Since the bumper is mounted at the bumper carrier proper, both parts must be replaced in case of a three-dimensional deformation.
A similar type of bumper is disclosed in DE 19849358A1. The crash absorbing element is directly integrated into the bumper carrier but not into the attachment of the bumper beam at the longitudinal beam of the vehicle. Locally varying values of flexural strength are realized by means of partial hardening of the bumper beam, whereby the non-hardened portions are able to take up the deformation as crash absorbing elements. This embodiment functions excellent when involved in a frontal impact situation, however, any case of a lateral impact causes much less deformation and thus it becomes much more likely that three-dimensional deformations occur. Such deformation is not going to be transmitted into the longitudinal beam, however also in this embodiment the bumper (which is not shown) and bumper beam must be provided with at least one deformation element which is integrated or which is configured as an additional assembly piece.
From the prior art as further disclosed in EP 894675A1 a bumper beam assembly including a bumper transverse beam incorporating several wall elements is disclosed. The spatial arrangement of the wall elements is configured as to provide impact force absorbing properties. However, the number of single parts still exceeds the number of parts disclosed in the previously discussed prior art. The bumper beam itself is not a unitary piece but is made from profiles that are assembled from four plates, which requires for a considerable number of production steps.
JP 11255049A discloses a bumper transverse beam with crash elements incorporated therein. Thus, a shortening of the distance between the longitudinal beam and the bumper surface is realized, however it is not quite obvious how the bumper beam can be dismantled from the longitudinal beam, in particular after impact when there are areas around the crash elements showing a three-dimensional deformation behavior.
It would therefore be desirable and advantageous to provide an improved bumper with means to obviate prior art shortcomings and to provide a bumper for absorbing deformations upon impact so as to prevent damage to the front end beam of the vehicle frame.